The production of large volume, high pressure, uniform glow discharges, which are stable at high power loading, has been a very difficult problem for a number of years. It has been by far the single most difficult task in E.D.L. (electric discharge laser) research and development. Toward the solution of this problem, considerable effort, both theoretical and experimental, has been expended over the past few years to define and extend the parameters that influence glow-to-arc transitions in a particular laser gas environment. Researchers such as Nighan et al. have shown that the "glow discharge", which is used to pump E.D.L.'s is inherently unstable, particularly in the carbon dioxide and halide systems [W. L. Nighan and W. J. Wiegand, "Instability Onset in Electron Beam Sustained K.sub.r F Laser Discharges", Appl. Phys. Lett. Vol. 32, No. 11, pp 730-733 (1978)]. A critical instability growth time can be ascribed to such discharges which specifies the maximum time duration that a laser discharge can be uniformly maintained to a given volume of gas before the onset of electro-thermal or electro metastable induced glow-to-arc transitions. Specific operational conditions such as gas species, mixture, pressure, power loading and flow velocity are found to have a profound influence on this critical instability formation period. A theoretical upper bound for the maximum power density that can be employed in conventionally stabilized laser discharges can be defined.
Historically, the actaul discharge power densities that could be employed without causing glow-to-arc transitions have fallen far short of the theoretical maximum.
As yet no economically satisfactory solution has been proposed to this difficulty.